Thin-film evaporator made of a corrosion resistant material

ABSTRACT

The invention relates to a thin-film evaporator equipped with a heatable tubular evaporator body in whose product charged interior a driven rotor is disposed which is equipped with essentially radially oriented vanes. The invention is formed from an evaporator body of at least one thick-wall graphite tube with a plurality of essentially axially extending bores disposed in the tube walls, each one of the bores open at the tube ends into an annular channel which is in communication with a connecting pipe stub for a heating medium. 
     Since the treatment of corrosive media, for example acids charged with solids, places high demands on corrosion resistance of the materials employed and additionally high demands for accuracy of the work, it is proposed to form the evaporator body (1) of at least one thick-wall graphite tube (2); to dispose a plurality of essentially axially extending bores (14) in the tube walls; and to have each one of the bores (14) open at the tube ends into an annular channel (15, 16) which is in communication with a connecting pipe stub (6, 9) for a heating medium.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a thin-film evaporator including a heatabletubular evaporator body with an externally driven rotor equipped withessentially radially oriented vanes being disposed in the productcharged interior of the evaporator body.

2. Description of the Related Art

Thin-film evaporator of the above-mentioned type are employed for theconcentration of viscous, temperature sensitive and/or coating formingsubstances. They are all based on the principle of producing, with theaid of a rotating rotor, a thin layer of the product in the interior ofa heated cylinder or cone so that the heat introduced through thecylinder wall leads to the evaporation of the liquid. The vapors needtraverse only a short path through the product. Thus it is possible toconcentrate solids containing liquids to high solids concentrations upto 80 weight % dry substance. The rotor is equipped with rigid vaneswhich are arranged with a narrow gap of a few millimeters from theheated wall or the rotor is equipped with movable wiper blades so thatthe product running over the heated walls of the evaporator body can berestricted to a thin film of product. When treating corrosive media, forexample for the concentration of acids charged with solids, thecorrosion problems cannot be solved with metal materials, particularlysince the evaporator body must also be designed as a pressure vessel.Tests with enamel coatings are able to solve the corrosion problem onlyin special cases, particularly since it is practically impossible inlarger units to perform the necessary mechanical work.

SUMMARY OF THE INVENTION

It is the object of the invention to configure a thin-film evaporator ofthe above-mentioned type so that the evaporator body has good corrosionresistance with good heat conductivity.

This is accomplished according to the invention in that the evaporatorbody is formed by at least one thick-walled tube of graphite; aplurality of essentially axially extending bores are disposed in thetube wall; and the bore openings at the tube ends each open into anannular channel which is in communication with a connecting pipe stubfor a heating medium. Surprisingly, it has been found that such anevaporator body made of a thick-walled graphite tube not only hasexcellent heat conducting properties but also permits the heating mediumto flow through it at high pressures. The interior of such a cylindricalor conical graphite tube can be worked properly and very precisely sothat it is possible with the aid of the rotor to apply a uniformly thinproduct film onto the interior wall of the tube as it is required forhigh evaporator output.

As an advantageous feature of the invention it is provided that theannular channel is configured as an open groove in a clamping ring thatcan be placed against the end face of the tube; the tube is held in asealed manner by way of spring-tensioned clamping anchors between twoclamping rings at its ends and the clamping rings are each provided witha connecting pipe stub for the heating medium, with the pipe stubopening into the associated groove. The clamping rings are here made ofmetal, preferably steel, with their interior faces that come in contactwith the product being coated or lined with corrosion resistantmaterials. Thus, corrosion resistance can also be realized in theseregions and advantage is taken of the fact that requirements forprecision are less in the regions of the clamping rings that lie outsideof the operating range of the rotor vanes. Due to the use of theclamping anchors, the graphite evaporator body is able to retain itssimple geometric shape, with the clamping anchors including the requiredclamping springs being configured in such a way that they are able towithstand the pressures exerted by the heating medium, that is, theykeep the clamping rings in close contact with the end faces of thegraphite tube.

As a further feature of the invention it is provided that the upperclamping ring, as the head ring, is equipped with an inlet pipe stub forthe product to be treated and with a discharge pipe stub for the vapors.Thus this component including the pipe stubs can be produced as a closedcomponent.

As another advantageous feature of the invention it is provided that thelower clamping ring, as the discharge ring, is equipped with an inwardlyprojecting circumferential conical collar.

Another, preferred feature of the invention provides that the rotorcomponent disposed in the interior of the evaporator body is composedessentially of a graphite core tube to which are fastened the vanes thatare produced of a graphite. Thus, it is ensured that the same processconditions are maintained for the evaporator region covered by the rotorvanes, on the one hand, and for the rotor itself. In this connection itis advisable, as a further feature, for the vanes to be formed by atleast three thin plates that are curved in the manner of a bowl andwhose longitudinal edges lie against one another and which are eachfastened by means of clamping screws in the peak region of the corepipe. In this connection it is advisable for the core pipe to be made ofgraphite and the vanes of a carbon fiber reinforced material, forexample, a carbon fiber reinforced plastic, so that the edges of thethin curved plates forming the vanes lie against one another undertension and reinforce one another.

As a further feature of the invention it is provided that thethick-walled tube forming the evaporator body and/or the core tube ofthe rotor and/or the rotor vanes are composed of a carbon fiberreinforced material. In this connection it is advisable to usecombinations so that, for example, the tube of the evaporator body ismade of graphite while the rotor is produced of a carbon fiberreinforced material, for example, a carbon fiber reinforced plastic. Theadvantage is that the rotor in particular with its components includingthe core pipe can be produced of thin-walled elements which are verystrong. This is of interest particularly if instead of rigid vanes, therotor is equipped with movable wiper blades. The term graphite in thesense of the present invention refers to fine-grained, porouselectrographite bodies which are made corrosion, temperature andpressure resistant by impregnation with high molecular synthetic resins.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in greater detail with reference toschematic drawings, in which:

FIG. 1 is a side view of a thin-film evaporator;

FIG. 2 is a partial longitudinal sectional view of the tubularevaporator body;

FIG. 3 depicts a rotor equipped with rigid vanes;

FIG. 4 is a sectional view of the rotor seen along line IV--IV of FIG.3;

FIG. 5 is a sectional view of the rotor seen along line V--V of FIG. 3;

FIG. 6 depicts a rotor having a solid rotor body; and

FIG. 7 depicts and end view of the tubular evaporator body with theclamping ring removed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The thin-film evaporator shown in FIG. 1 is essentially composed of anevaporator body 1 equipped with a thick-walled graphite tube whoseconfiguration will be described in greater detail in connection withFIG. 2. By means of a lower clamping ring 4 and an upper clamping ring 3and with the aid of a plurality of clamping rods 5 that are distributeduniformly around its circumference, the ends of thick-walled tube 2 areurged against the rings 3 and 4.

The upper clamping ring 3 is here configured as a head ring and itsregion lying directly against tube 2 is equipped with a connecting pipestub 6 for the introduction of a heating medium. The head ring isfurther provided with an inlet pipe stub 7 for the product to be treatedand with a discharge pipe stub 8 for the discharge of the vaporsgenerated in the evaporation process. Clamping ring 4 in turn isprovided with a connecting pipe stub 9 through which the heating mediumis extracted. The configuration of head ring 3 and discharge ring 4 willbe described in greater detail below with reference to the sectionalview of FIG. 2.

Head ring 3 is followed at the top by a housing 10 through which passthe bearing and the seal for the shaft of the rotor disposed in thethin-film evaporator. A drive motor 11 is supported on housing 10 by wayof a shaft protecting tube 12. The entire arrangement is supported byway of head ring 3 on a supporting flange 13 and is releasably connectedwith the latter. The concentrated product leaves through the dischargeopening formed by discharge ring 4.

As can be seen in the partial vertical longitudinal sectional view ofevaporator body 1 shown in FIG. 2, tube 2 is given relatively thickwalls and these walls are provided with a plurality of axially parallelbores 14 (FIG. 7). Each one of bores 14 opens at its end face into agroove 15 in head ring 3 and into a groove 16 in discharge ring 4, withthese grooves forming an annular channel into which open the connectingpipe stubs 6 and 9 for the heating medium. Head ring 3 and dischargering 4 are tightly clamped to tube 2 by means of tension rods 5 andseals 17 placed therebetween, with the thermal expansion of tube 2 beingabsorbed by way of a pre-tensioned spring packet 18. On their facescoming in contact with the product, head ring 3 and discharge ring 4 areprovided with a corrosion resistant coating 3' and 4'.

The rotor 19, which is shown only as a half-section, is disposed in theinterior. At the upper end of the rotor, a connecting shaft 20 is incommunication with drive motor 11. The essentially tubular rotor, whoseconfiguration will be described in greater detail in connection withFIGS. 3, 4, and 5, is provided with vanes 21. As shown in FIG. 2, vanes21 cover only the region of tube 2. In the region of head ring 3, rotor19 is terminated at the top by a charging ring 22 which is delimited byan upper and lower edge web 23 so that an annular chamber 24 is formedthere into which opens the inlet pipe stub 7 for the product to betreated so that the product is able to enter in the form of a thin filminto tube 2 and thus into the effective range of rotor vanes 21. Theresulting vapors are extracted through discharge pipe stub 8 which,depending on the process, also serves to produce a vacuum in theinterior of the thin-film evaporator.

FIG. 3 is a side view showing the entire rotor. The rotor is essentiallycomposed of a core tube 25 onto which vanes 21 are placed in a manner tobe described in greater detail below. Charging ring 22 terminates theregion occupied by vanes 21 at the top. Above charging ring 22, coretube 25 is connected to a drive shaft 26 that is connected with drivemotor 11 and is made of steel in the conventional manner since thisregion of the rotor is disposed above the housing 10 provided with theseals. In contrast thereto, core tube 25 is made of graphite or a carbonfiber reinforced material.

The configuration is shown in FIG. 4 which is a sectional view to alarger scale seen along line IV--IV of FIG. 3. Core tube 25 is hereprovided with a plurality of bores over its length which intersect in aspaced arrangement and through which clamping screws 27 can then beplaced. The outer ends of the clamping screws are shown schematically inFIG. 3.

In the illustrated embodiment, rotor vanes 21 are formed by fourbowl-shaped curved thin plates 28 whose longitudinal edges lie againstone another, with clamping screws 27 in peak region 29 pressing theplates against core tube 25. As indicated by the top view shown in FIG.5 onto charging ring 22, approximately star-shaped plates 30 areprovided at both ends, with the lower plate covering the space betweencore tube 25 and the interior of plate 28. The space 31 remaining in theinterior between edge web 23 serves as a passage channel for the vaporsto be extracted. The top view of FIG. 5 further shows that the outeredges 32 of vanes 21 project only slightly beyond the outer edge 33 ofedge webs 23.

As indicated in the sectional view of FIG. 6, rotor 19 may also beprovided with a solid, graphite rotor body 34 that has an approximatelystar-shaped cross section and whose end face edges 35 are provided withpreferably exchangeable edge elements 36. These edge elements whichextend over the length of rotor body 34 and are composed of one or aplurality of juxtaposed components are likewise made of a corrosionresistant material, for example a carbon fiber reinforced material. Edgeelements 36 may here be rigid or may be connected with rotor body 34 inthe form of movable wiper blades.

We claim:
 1. A heatable thin-film evaporator, comprising:an externallydriven rotor with essentially radially oriented vanes disposed in atubular evaporator body; the evaporator body, including at least onethick-walled graphite tube having a first end face and a second endface, a plurality of bores extending essentially axially between thefirst and second end faces, a first clamping ring having a first edgeand a second edge, the first edge including a first open groove annularchannel, the first end face of the evaporator body being coupled to thefirst clamping ring so that the plurality of bores open into the firstopen groove annular channel; a second clamping ring having a first edgeand a second edge, the first edge including a second open groove annularchannel in the first edge, the first edge of the second clamping ringcoupled to the second end face of the evaporator body so that theplurality of bores open into the second open groove annular channel; aplurality of tension rods, each tension rod having a first end coupledto the first clamping ring and a second end coupled to the secondclamping ring by a spring arrangement so that the first and second endfaces of the tube are held in a sealing manner between the first andsecond clamping rings; a first connecting pipe, in communication withthe first open groove annular channel, for carrying a heating medium;and a second connecting pipe, in communication with the second opengroove annular channel, for carrying the heating medium.
 2. A thin-filmevaporator according to claim 1, wherein the first clamping ring isconfigured as a head ring and is provided with an inlet pipe for aproduct to be treated and with a discharge pipe for vapors.
 3. Athin-film evaporator according to claim 1, where the second clampingring is provided with an inwardly projecting circumferential, conicalcollar.
 4. A thin-film evaporator according to claim 1, wherein thefirst clamping ring and the second clamping ring are made of metal, andeach clamping ring being provided with a corrosion resistant coating onan inner surface of the clamping ring.
 5. A thin-film evaporatoraccording to claim 1, wherein the rotor has a core tube and wherein thevanes are fastened to the core tube.
 6. A thin-film evaporator accordingto claim 5, wherein the vanes are formed from at least three curved thinplates, each plate having longitudinal edges and a peak region, theplates lying against one another along their respective longitudinaledges, and each plate being fastened to the core tube at its peakregion.
 7. A thin-film evaporator according to claim 1, wherein therotor has a periphery provided with removable corrosion resistant edgeelements rigidly connected with the rotor.
 8. A thin-film evaporatoraccording to claim 7, wherein the rotor includes a rotor body formedfrom graphite, and the removable corrosion resistant edge elements beingrigidly connected to the rotor body.
 9. A thin-film evaporator accordingto claim 5, wherein the core tube and the vanes are formed fromgraphite.
 10. A thin-film evaporator according to claim 5, wherein thecore tube is composed of a carbon fiber reinforced material.
 11. Athin-film evaporator according to claim 10, wherein the vanes arecomposed of a carbon fiber reinforced material.
 12. A thin-filmevaporator according to claim 7, wherein the rotor includes a rotor bodyformed from graphite, and the removable corrosion resistant edgeelements being movably connected to the rotor body.
 13. A thin-filmevaporator according to claim 1, wherein the rotor includes a peripheryprovided with removable corrosion resistant edge elements movablyconnected with the rotor.